Liquid ejection apparatus, liquid ejection system, and liquid ejection method

ABSTRACT

A liquid ejection apparatus includes a plurality of liquid ejection head units that eject liquid onto a conveyed object at different positions along a conveying path; a first support member and a second support member that are respectively provided at an upstream side and a downstream side of a landing position of liquid ejected by a corresponding liquid ejection head unit; a first detection unit that is installed between the first support member and the second support member and is configured to detect a position of the conveyed object in a direction orthogonal to a conveying direction of the conveyed object; a second detection unit that is installed upstream of the first detection unit; and a movement control unit that moves each liquid ejection head unit based on a plurality of detection results output by the first detection unit and/or the second detection unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application and claimspriority under 35 U.S.C. 120 to U.S. patent application Ser. No.16/243,399 filed on Jan. 9, 2019, which is a continuation application ofU.S. patent application Ser. No. 15/382,963 filed on Dec. 19, 2016,which claims priority under 35 U.S.C. § 119 to Japanese PatentApplication No. 2015-255355 filed on Dec. 25, 2015 and Japanese PatentApplication No. 2016-231594 filed on Nov. 29, 2016. The entire contentsof foregoing applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to a liquid ejection apparatus, a liquidejection system, and a liquid ejection method.

2. Description of the Related Art

Techniques for forming an image using the so-called inkjet method thatinvolves ejecting ink from a print head are known. Also, techniques areknown for improving the print quality of an image printed on a printmedium using such image forming techniques.

For example, a method for improving print quality by adjusting theposition of a print head is known. Specifically, such method involvesusing a sensor to detect positional variations in a transverse directionof a web corresponding to a print medium that passes through acontinuous paper printing system. The method further involves adjustingthe position of the print head in the transverse direction in order tocompensate for the positional variations detected by the sensor (e.g.,see Japanese Unexamined Patent Publication No. 2015-13476).

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, a liquid ejectionapparatus is provided that includes a plurality of liquid ejection headunits that are configured to eject liquid onto a conveyed object atdifferent positions along a conveying path for conveying the conveyedobject, a first support member that supports the conveyed object and isprovided upstream of a landing position of the liquid ejected onto theconveyed object by a corresponding liquid ejection head unit of theplurality of liquid ejection head units, a second support member thatsupports the conveyed object and is provided downstream of the landingposition of the corresponding liquid ejection head unit, at least onefirst detection unit that is installed between the first support memberand the second support member and is configured to detect a position ofthe conveyed object with respect to an orthogonal direction that isorthogonal to a conveying direction of the conveyed object, at least onesecond detection unit that is installed upstream of the first detectionunit and is configured to detect the position of the conveyed objectwith respect to the orthogonal direction, and a movement control unitthat is configured to move each liquid ejection head unit of theplurality of liquid ejection head units based on at least two detectionresults selected from a plurality of detection results output by thefirst detection unit and the second detection unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a liquid ejection apparatusaccording to an embodiment of the present invention;

FIG. 2 is a schematic diagram illustrating an example overallconfiguration of the liquid ejection apparatus according to anembodiment of the present invention;

FIGS. 3A and 3B are diagrams illustrating an example externalconfiguration of a liquid ejection head according to an embodiment ofthe present invention;

FIG. 4 is an external view of a detection device according to anembodiment of the present invention;

FIG. 5 is a block diagram illustrating an example functionalconfiguration of the detection unit for implementing a correlationcalculation according to an embodiment of the present invention;

FIG. 6 is a diagram illustrating an example method of searching for apeak position in the correlation calculation according to an embodimentof the present invention;

FIG. 7 is a diagram illustrating an example calculation result ofimplementing the correlation calculation according to an embodiment ofthe present invention;

FIG. 8 is a block diagram illustrating an example functionalconfiguration of the detection unit according to an embodiment of thepresent invention;

FIGS. 9A and 9B are diagrams illustrating example variations in theposition of a recording medium with respect to an orthogonal direction;

FIG. 10 is a diagram illustrating an example cause of a color shift;

FIG. 11 is a block diagram illustrating an example hardwareconfiguration of a control unit according to an embodiment of thepresent invention;

FIG. 12 is a block diagram illustrating an example hardwareconfiguration of a data management device included in the control unitaccording to an embodiment of the present invention;

FIG. 13 is a block diagram illustrating an example hardwareconfiguration of an image output device included in the control unitaccording to an embodiment of the present invention;

FIG. 14 is a flowchart illustrating an example overall processimplemented by the liquid ejection apparatus according to an embodimentof the present invention;

FIG. 15 is a block diagram illustrating an example hardwareconfiguration for calculating an amount of positional variationaccording to an embodiment of the present invention;

FIG. 16 is a diagram illustrating an example moving mechanism for movinga liquid ejection head unit of the liquid ejection apparatus accordingto an embodiment of the present invention;

FIG. 17 is a timing chart illustrating an example method for calculatingan amount of positional variation of a conveyed object that isimplemented by the liquid ejection apparatus according to an embodimentof the present invention;

FIG. 18 is a diagram illustrating a test pattern used by the liquidejection apparatus according to an embodiment of the present invention;

FIG. 19 is a diagram illustrating an example installation position of afirst sensor in the liquid ejection apparatus according to an embodimentof the present invention;

FIG. 20 is a diagram illustrating an example hardware configuration of aliquid ejection apparatus according to a first comparative example;

FIG. 21 is a diagram illustrating an example processing result of anoverall process implemented by the liquid ejection apparatus accordingto the first comparative example;

FIG. 22 is a diagram illustrating an example processing result of anoverall process implemented by a liquid ejection apparatus according toa second comparative example;

FIG. 23 is a diagram illustrating an example installation position of asensor in a liquid ejection apparatus according to a third comparativeexample;

FIG. 24 is a block diagram illustrating an example functionalconfiguration of the liquid ejection apparatus according to anembodiment of the present invention; and

FIG. 25 is a schematic diagram illustrating an example modification ofthe liquid ejection apparatus according to an embodiment of the presentinvention.

DESCRIPTION OF THE EMBODIMENTS

One aspect of the present invention is directed to providing a liquidejection apparatus that is capable of improving accuracy of a landingposition of ejected liquid in a direction orthogonal to a conveyingdirection of a conveyed object.

In the following, embodiments of the present invention are describedwith reference to the accompanying drawings. Note that elementsdescribed in the present description and the drawings that havesubstantially identical functional features are given the same referencenumerals and overlapping explanations may be omitted.

<Overall Configuration>

FIG. 1 is a schematic diagram illustrating an example liquid ejectionapparatus according to an embodiment of the present invention. Forexample, a liquid ejection apparatus according to an embodiment of thepresent invention may be an image forming apparatus 110 as illustratedin FIG. 1. Liquid ejected by such an image forming apparatus 110 may berecording liquid, such as aqueous ink or oil-based ink, for example.Hereinafter, the image forming apparatus 110 is described as an exampleliquid ejection apparatus according to an embodiment of the presentinvention.

A conveyed object conveyed by the image forming apparatus 110 may be arecording medium, for example. In the illustrated example, the imageforming apparatus 110 ejects liquid on a web 120 corresponding to anexample of a recording medium that is conveyed by a roller 130 to forman image thereon. Also, note that the web 120 may be a so-calledcontinuous paper print medium, for example. That is, the web 120 may bea rolled sheet that is capable of being wound up, for example. Thus, theimage forming apparatus 110 may be a so-called production printer. Inthe following, an example is described where the roller 130 adjusts thetension of the web 120 and conveys the web 120 in a direction indicatedby arrow 10 (hereinafter referred to as “conveying direction 10”).Further, a direction orthogonal to the conveying direction 10 asindicated by arrow 20 in FIG. 1 is referred to as “orthogonal direction20”. In the present example, it is assumed that the image formingapparatus 110 corresponds to an inkjet printer that forms an image onthe web 120 by ejecting inks in four different colors, including black(K), cyan (C), magenta (M), and yellow (Y), at predetermined portions ofthe web 120.

FIG. 2 is a schematic diagram illustrating an example overallconfiguration of the liquid ejection apparatus according to anembodiment of the present invention. In FIG. 2, the image formingapparatus 110 includes four liquid ejection head units for ejecting inksin the above four different colors.

Each liquid ejection head unit ejects ink in a corresponding color onthe web 120 that is being conveyed in the conveying direction 10. Also,the web 120 is conveyed by two pairs of nip rollers NR1 and NR2, aroller 230, and the like. Hereinafter, the pair of nip rollers NR1 thatis arranged upstream of the liquid ejection head units is referred to as“first nip rollers NR1”. On the other hand, the pair of nip rollers NR2that is arranged downstream of the first nip rollers NR1 and the liquidejection head units is referred to as “second nip rollers NR2”. Eachpair of the nip rollers NR1 and NR2 is configured to rotate whileholding a conveyed object, such as the web 120, therebetween. Asdescribed above, the first and second nip rollers NR1 and NR2 and theroller 230 may constitute a mechanism for conveying the web 120 in apredetermined direction.

Note that a recording medium to be conveyed, such as the web 120, ispreferably relatively long. Specifically, the length of the recordingmedium is preferably longer than the distance between the first niprollers NR1 and the second nip rollers NR2. Further, note that therecording medium is not limited to the web 120. For example, therecording medium may also be a folded sheet, such as the so-called “Zpaper” that is stored in a folded state.

In the present example, it is assumed that the liquid ejection headunits for the four different colors are arranged in the following orderfrom the upstream side to the downstream side: black (K), cyan (C),magenta (M), and yellow (Y). That is, the liquid ejection head unit forblack (K) (hereinafter referred to as “black liquid ejection head unit210K”) is installed at the most upstream side. The liquid ejection headunit for cyan (C) (hereinafter referred to as “cyan liquid ejection headunit 210C”) is installed next to the black liquid ejection head unit210K. The liquid ejection head unit for magenta (M) (hereinafterreferred to as “magenta liquid ejection head 210M”) is installed next tothe cyan liquid ejection head unit 210C. The liquid ejection head unitfor yellow (Y) (hereinafter referred to as “yellow liquid ejection headunit 210Y”) is installed at the most downstream side.

The liquid ejection head units 210K, 210C, 210M, and 210Y are configuredto eject ink in their respective colors on predetermined portions of theweb 120 based on image data, for example. A position at which ink isejected (hereinafter referred to as “landing position”) may besubstantially the same as the position where the ink ejected from theliquid ejection head unit lands on the recording medium; i.e., directlybelow the liquid ejection head unit. In the present example, black inkis ejected onto a landing position of the black liquid ejection headunit 210K (hereinafter referred to as “black landing position PK”).Similarly, cyan ink is ejected onto a landing position of the cyanliquid ejection head unit 210C (hereinafter referred to as “cyan landingposition PC”). Further, magenta ink is ejected onto a landing positionof the magenta liquid ejection head unit 210M (hereinafter referred toas “magenta landing position PM”). Also, yellow ink is ejected onto alanding position of the yellow liquid ejection head unit 210Y(hereinafter referred to as “yellow landing position PY”). Note that thetiming at which each of the liquid ejection head units ejects ink may becontrolled by a controller 520 that is connected to each of the liquidejection head units.

Also, multiple rollers are installed with respect to each of the liquidejection head units. For example, rollers may be installed at theupstream side and the downstream side of each of the liquid ejectionhead units. In the example illustrated in FIG. 2, a roller used toconvey the web 120 to the landing position of a liquid ejection headunit (hereinafter referred to as “first roller”) is disposed on theupstream side of each liquid ejection head unit. Also, a roller used toconvey the web 120 downstream from the landing position (hereinafterreferred to as “second roller”) is disposed on the downstream side ofeach liquid ejection head unit. By arranging the first roller and thesecond roller at the upstream side and downstream side of the landingposition of each liquid ejection head unit, the so-called “fluttering”effect may be reduced, for example. Note that the first roller and thesecond roller are examples of support members used to convey therecording medium and may be driven rollers, for example. The firstroller and the second roller may be also be drive rollers, for example.

Note that the first roller, as an example of a first support member, andthe second roller, as an example of a second support member, do not haveto be rotating bodies and may be driven rollers, for example. That is,any suitable member capable of supporting a conveyed object may be usedas the first roller and the second roller. For example, a pipe or ashaft having a circular cross-sectional shape may be used as the firstsupport member and the second roller support member. Also, in anotherexample, a curved plate having an arc-shaped portion that comes intocontact with a conveyed object may be used as the first support memberand the second support member. In the following, the first roller isdescribed as an example of a first support member and the second rolleris described as an example of a second support member.

Specifically, with respect to the black liquid ejection head unit 210K,a first roller CR1K used for conveying the web 120 to the black landingposition PK to eject black ink onto a predetermined portion of the web120 is arranged at the upstream side of the black liquid ejection headunit 210K. Also, a second roller CR2K used for conveying the web 120further downstream of the black landing position PK is arranged at thedownstream side of the black liquid ejection head unit 210K. Similarly,a first roller CR1C and a second roller CR2C are respectively arrangedat the upstream side and downstream side of the cyan liquid ejectionhead unit 210C. Further, a first roller CR1M and a second roller CR2Mare respectively arranged at the upstream side and downstream side ofthe magenta liquid ejection head unit 210M. Further, a first roller CR1Yand a second roller CR2Y are respectively arranged at the upstream sideand downstream side of the yellow liquid ejection head unit 210Y.

In the following, an example external configuration of the liquidejection head units is described with reference to FIGS. 3A and 3B.

FIG. 3A is a schematic plan view of the four liquid ejection head units210K, 210C, 210M, and 210Y included in the image forming apparatus 110according to the present embodiment. FIG. 3B is an enlarged plan view ofa head 210K-1 of the liquid ejection head unit 210K for ejecting black(K) ink.

In FIG. 3A, the liquid ejection head units are full-line type headunits. That is, the image forming apparatus 110 has the four liquidejection head units 210K, 210C, 210M, and 210Y for the four differentcolors, black (K), cyan (C), magenta (M), and yellow (Y), arranged inthe above recited order from the upstream side to the downstream side inthe conveying direction 10.

The liquid ejection head unit 210K for ejecting black (K) ink includesfour heads 210K-1, 210K-2, 210K-3, and 210K-4, arranged in a staggeredmanner in the orthogonal direction 20 orthogonal to the conveyingdirection 10. This enables the image forming apparatus 110 to form animage across the entire width of an image forming region (print region)of the web 120. Note that the configurations of the other liquidejection head units 210C, 210M, and 210Y may be similar to that of theliquid ejection head unit 210K, and as such, descriptions thereof willbe omitted.

Note that although an example where the liquid ejection head unit ismade up of four heads is described above, the liquid ejection head unitmay also be made up of a single head, for example.

<Detection Unit>

In the present embodiment, a sensor as an example of a detection unitfor detecting a position of a recording medium in the orthogonaldirection is installed in the liquid ejection apparatus in addition tosensors that are installed for the respective liquid ejection headunits. In the example illustrated in FIG. 2, four sensors SENK, SENC,SENM, and SENY are respectively installed for the four liquid ejectionhead units 210K, 210C, 210M, and 210Y. In addition, one sensor SEN2 isinstalled upstream of the above four sensors. That is, a total of fivesensors are installed in the liquid ejection apparatus illustrated inFIG. 2. Note that in the following descriptions, the sensors that areinstalled for the respective liquid ejection head units are referred toas “first sensors”, and the sensor that is installed upstream of thefirst sensors is referred to as “second sensor”. Also, the first andsecond sensors may generically be referred to as “sensor(s)”.

In the following, an example case where a total of five sensors areprovided in the liquid ejection apparatus is described. Note, however,that the total number of sensors is not limited to such a number. Thatis, the total number of the first and second sensors may be any numbergreater than the total number of liquid ejection head units provided inthe liquid ejection apparatus. For example, two or more first sensorsmay be provided with respect to each of the liquid ejection head units.Similarly, two or more second sensors may be provided upstream of thefirst sensors, for example.

The sensor may be a laser sensor, a pneumatic sensor, a photoelectricsensor, an ultrasonic sensor, or an optical sensor that uses light suchas infrared light, for example. Note that an example of an opticalsensor includes a CCD (Charge Coupled Device) camera. That is, thesensor constituting the first/second detection unit may be a sensor thatis capable of detecting the edge of the recording medium, for example.Note that the first and second sensors may all be the same type ofsensor, or they may be different types of sensors. In the following, itis assumed that all the sensors are of the same type. Also, each sensormay have a configuration as described below, for example.

FIG. 4 is an external view of an example detection device (sensor)implementing the detection unit according to an embodiment of thepresent invention.

The sensor illustrated in FIG. 4 performs detection by capturing animage of a speckle pattern that is formed when light from a light sourceis incident on a conveyed object, such as the web 120, for example.Specifically, the sensor includes a semiconductor laser diode (LD) andan optical system such as a collimator lens (CL). Further, the sensorincludes a CMOS (Complementary Metal Oxide Semiconductor) image sensorfor capturing an image of a speckle pattern and a telecentric opticalimaging system (telecentric optics) for imaging the speckle pattern onthe CMOS image sensor.

In the example illustrated in FIG. 4, for example, the CMOS image sensormay capture an image of the speckle pattern multiple times, such as attime t1 and at time t2. Then, based on the image captured at time t1 andthe image captured at time t2, a calculating device, such as a FPGA(Field-Programmable Gate Array) circuit, may perform a process such ascross-correlation calculation. Then, based on the movement of thecorrelation peak position calculated by the correlation calculation, thesensor may output the amount of movement of the conveyed object fromtime t1 to time t2, for example. Note that in the illustrated example,it is assumed that the width (W)×depth (D)×height (H) dimensions of thesensor is 15 mm×60 mm×32 mm. Also, note that the CMOS image sensor is anexample of hardware for implementing an imaging unit, and the FPGAcircuit is an example of a calculating device.

Also, the correlation calculation may be performed in the followingmanner, for example.

<Correlation Calculation>

FIG. 5 is a diagram illustrating an example correlation calculationmethod implemented by the detection unit according to an embodiment ofthe present invention. For example, the detection unit may perform acorrelation calculation operation as illustrated in FIG. 5 to calculatea relative position of the web 120 with respect to the position of asensor, an amount of movement of the web 120, and/or the moving speed ofthe web 120.

In the example illustrated in FIG. 5, the detection unit includes afirst two-dimensional Fourier transform unit FT1, a secondtwo-dimensional Fourier transform unit FT2, a correlation image datagenerating unit DMK, a peak position search unit SR, a calculating unitCAL, and a transform result storage unit MEM.

The first two-dimensional Fourier transform unit FT1 transforms firstimage data D1. Specifically, the first two-dimensional Fourier transformunit FT1 includes a Fourier transform unit FT1 a for the orthogonaldirection and a Fourier transform unit FT1 b for the conveyingdirection.

The Fourier transform unit FT1 a for the orthogonal direction applies aone-dimensional Fourier transform to the first image data D1 in theorthogonal direction. Then, the Fourier transform unit FT1 b for theconveying direction applies a one-dimensional Fourier transform to thefirst image data D1 in the conveying direction based on the transformresult obtained by the Fourier transformation unit FT1 a for theorthogonal direction. In this way, the Fourier transform unit FT1 a forthe orthogonal direction and the Fourier transform unit FT1 b for theconveying direction may respectively apply one-dimensional Fouriertransforms in the orthogonal direction and the conveying direction. Thefirst two-dimensional Fourier transform unit FT1 then outputs thetransform result to the correlation image data generating unit DMK.

Similarly, the second two-dimensional Fourier transform unit FT2transforms second image data D2. Specifically, the secondtwo-dimensional Fourier transform unit FT2 includes a Fourier transformunit FT2 a for the orthogonal direction, a Fourier transform unit FT2 bfor the conveying direction, and a complex conjugate unit FT2 c.

The Fourier transform unit FT2 a for the orthogonal direction applies aone-dimensional Fourier transform to the second image data D2 in theorthogonal direction. Then, the Fourier transformation unit FT2 b forthe conveying direction applies a one-dimensional Fourier transformationto the second image data D2 in the conveying direction based on thetransform result obtained by the Fourier transformation unit FT2 a forthe orthogonal direction. In this way, the Fourier transform unit FT2 afor the orthogonal direction and the Fourier transform unit FT2 b forthe conveying direction may respectively apply one-dimensional Fouriertransforms in the orthogonal direction and the conveying direction.

Then, the complex conjugate unit FT2 c calculates the complex conjugateof the transform results obtained by the Fourier transform unit FT2 afor the orthogonal direction and the Fourier transform unit FT2 b forthe conveying direction. Then, the second two-dimensional Fouriertransform unit FT2 outputs the complex conjugate calculated by thecomplex conjugate unit FT2 c to the correlation image data generatingunit DMK.

Then, the correlation image data generating unit DMK compares thetransform result of the first image data D1 output by the firsttwo-dimensional Fourier transform unit FT1 and the transform result ofthe second image data D2 output by the second two-dimensional Fouriertransform unit FT2.

The correlation image data generating unit DMK includes an integrationunit DMKa and a two-dimensional inverse Fourier transform unit DMKb.

The integration unit DMKa integrates the transform result of the firstimage data D1 and the transform result of the second image data D2. Theintegration unit DMKa then outputs the integration result to thetwo-dimensional inverse Fourier transform unit DMKb.

The two-dimensional inverse Fourier transform unit DMKb applies atwo-dimensional inverse Fourier transform to the integration resultobtained by the integration unit DMKa. By applying the two-dimensionalinverse Fourier transform to the integration result in theabove-described manner, correlation image data may be generated. Then,the two-dimensional inverse Fourier transform unit DMKb outputs thegenerated correlation image data to the peak position search unit SR.

The peak position search unit SR searches the generated correlationimage data to find a peak position of a peak luminance (peak value) witha steepest rise and fall. That is, first, a value indicating theintensity of light, i.e., luminance, is input to the correlation imagedata. Also, the luminance is input in the form of a matrix.

In the correlation image data, the luminance is arranged at intervals ofthe pixel pitch (pixel size) of an area sensor. Thus, the search for thepeak position is preferably performed after the so-called sub-pixelprocessing is performed. By performing the sub-pixel processing, thepeak position may be searched with high accuracy. Thus, the detectionunit may be able to accurately output the relative position, the amountof movement, and/or the moving speed of the web 120, for example.

Note that the search by the peak position search unit SR may beimplemented in the following manner, for example.

FIG. 6 is a diagram illustrating an example peak position search methodthat may be implemented in the correlation calculation according to anembodiment of the present invention. In the graph of FIG. 6, thehorizontal axis indicates a position in the conveying direction of animage represented by the correlation image data. The vertical axisindicates the luminance of the image represented by the correlationimage data.

In the following, an example using three data values, i.e., first datavalue q1, second data value q2, and third data value q3, of theluminance values indicated by the correlation image data will bedescribed. That is, in this example, the peak position search unit SR(FIG. 5) searches for a peak position P on a curve k connecting thefirst data value q1, the second data value q2, and the third data valueq3.

First, the peak position search unit SR calculates differences inluminance of the image represented by the correlation image data. Then,the peak position search unit SR extracts a combination of data valueshaving the largest difference value from among the calculateddifferences. Then, the peak position search unit SR extractscombinations of data values that are adjacent to the combination of datavalues with the largest difference value. In this way, the peak positionsearch unit SR can extract three data values, such as the first datavalue q1, the second data value q2, and the third data value q3, asillustrated in FIG. 20. Then, by obtaining the curve k by connecting thethree extracted data values, the peak position search unit SR may beable to search for the peak position P. In this way, the peak positionsearch unit SR may be able to reduce the calculation load for operationssuch as sub-pixel processing and search for the peak position P athigher speed, for example. Note that the position of the combination ofdata values with the largest difference value corresponds to thesteepest position. Also, note that sub-pixel processing may beimplemented by a process other than the above-described process.

When the peak position search unit SR searches for a peak position inthe manner described above, the following calculation result may beobtained, for example.

FIG. 7 is a diagram illustrating an example calculation result of thecorrelation calculation according to an embodiment of the presentinvention. FIG. 7 indicates a correlation level distribution of across-correlation function. In FIG. 7, the X-axis and the Y-axisindicate serial numbers of pixels. The peak position search unit SR(FIG. 5) searches the correlation image data to find a peak position,such as “correlation peak” as illustrated in FIG. 7, for example.

Referring back to FIG. 5, the calculating unit CAL may calculate therelative position, the amount of movement, and/or the moving speed ofthe web 120, for example. Specifically, for example, the calculatingunit CAL may calculate the relative position and the amount of movementof the web 120 by calculating the difference between a center positionof the correlation image data and the peak position identified by thepeak position search unit SR.

Also, based on the relative position, the calculating unit CAL maycalculate the moving speed of the web 120 using the following equation(1), for example.

V=[{(K+J)×L}/√{square root over (i)}]/T  (1)

In the above equation (1), V represents the moving speed. T representsthe imaging cycle at which an image is captured. Also, K represents therelative pixel number. Further, L represents the pixel pitch, and Jrepresents the relative position. Also, i represents the magnificationof the area sensor.

As described above, by performing the correlation calculation, thedetection unit may be able to detect the relative position, the amountof movement, and/or the moving speed of the web 120, for example. Note,however, that the method of detecting the relative position, the amountof movement, and the moving speed is not limited to the above-describedmethod. For example, the detection unit may also detect the relativeposition, the amount of movement, and/or the moving speed in the manneras described below.

First, the detection unit binarizes the first image data and the secondimage data based on their luminance. In other words, the detection unitsets a luminance to “0” if the luminance is less than or equal to apreset threshold value, and sets a luminance to “1” if the luminance isgreater than the threshold value. By comparing the binarized first imagedata and binarized second image data, the detection unit may detect therelative position, for example.

Note that the detection unit may detect the relative position, theamount of movement, and/or the moving speed using other detectionmethods as well. For example, the detection unit may detect the relativeposition based on patterns captured in two or more sets of image datausing a so-called pattern matching process or the like.

FIG. 8 is a block diagram illustrating an example functionalconfiguration of the detection unit according to an embodiment of thepresent invention. In FIG. 8, the detection unit includes an imagingunit 110F1, an imaging control unit 110F2, a storage unit 110F3, and aspeed calculating unit 110F4.

In the following, an example case is described where an imaging processis performed two times by the imaging unit 110F1, i.e., a case where twoimages are generated by the imaging unit 110F1. Also, in the followingdescriptions, the position at which the first imaging process isperformed on the web 120 is referred to as “position A”. Further, it isassumed that the second imaging process on the web 120 is performed atthe time a pattern captured in the image obtained at “position A” in thefirst imaging process is moved to “position B” as a result of the web120 being conveyed in the conveying direction 10.

As illustrated in FIG. 8, the imaging unit 110F1 captures an image of aconveyed object such as the web 120 that is conveyed in the conveyingdirection 10.

The imaging control unit 110F2 includes an image acquiring unit 110F21and a shutter control unit 110F22.

The image acquiring unit 110F21 acquires an image captured by theimaging unit 110F1.

The shutter control unit 110F22 controls the timing at which the imagingunit 110F1 captures an image.

The storage unit 110F3 includes a first storage area 110F31 and a secondstorage area 110F32.

An image captured when the pattern of the web 120 is located at“position A” and an image captured when the pattern is located at“position B” are respectively stored in the first storage area 110F31and the second storage area 110F32.

The speed calculating unit 110F4 is capable of obtaining the position ofthe imaged pattern of the web 120, the moving speed of the web 120 beingconveyed, and the amount of movement of the web 120 being conveyed,based on the images stored in the first storage area 110F31 and thesecond storage area 110F32. For example, the speed calculating unit110F4 may output to the shutter control unit 110F22, data such as a timedifference Δt indicating the timing for releasing a shutter. That is,the speed calculating unit 110F4 may output a trigger signal to theshutter control unit 110F22 so that the image representing “position A”and the image representing “position B” may be captured at differenttimings having the time difference of Δt, for example. Then, the speedcalculating unit 110F4 may control a motor or the like that is used toconvey the web 120 so as to achieve the calculated moving speed.

The web 120 is a member having scattering properties on its surface orin its interior, for example. Thus, when laser light is irradiated onthe web 120, the laser light is diffusely reflected by the web 120. Bythis diffuse reflection, a pattern is formed on the web 120. The patternmay be a so-called speckle pattern including speckles (spots), forexample. Thus, when the web 120 is imaged, an image representing aspeckle pattern may be obtained. Because the position of the specklepattern can be determined based on the obtained image, the detectionunit may be able to detect where a predetermined position of the web 120is located. Note that the speckle pattern is generated by theinterference of irradiated laser beams caused by a roughness of thesurface or the interior of the web 120, for example.

Also, the light source is not limited to an apparatus using laser light.For example, the light source may be an LED (Light Emitting Diode) or anorganic EL (Electro-Luminescence) element. Also, depending on the typeof light source used, the pattern formed on the web 120 may not be aspeckle pattern. In the example described below, it is assumed that thepattern is a speckle pattern.

When the web 120 is conveyed, the speckle pattern of the web 120 is alsoconveyed. Therefore, the amount of movement of the web 120 may beobtained by detecting the same speckle pattern at different times. Thatis, by detecting the same speckle pattern multiple times to obtain theamount of movement of the speckle pattern, the speed calculating unit110F4 may be able to obtain the amount of movement of the web 120.Further, the speed calculating unit 110F4 may be able to obtain themoving speed of the web 120 by converting the above obtained amount ofmovement into a distance per unit time, for example.

In this way, based on the speckle pattern, the image forming apparatus110 may be able to obtain accurate detection results indicating theposition of the web 120 in the orthogonal direction, for example.

Note that the detection unit may be configured to detect the position ofthe web 120 in the conveying direction, for example. That is, thedetection unit may be used to detect a position in the conveyingdirection as well as a position in the orthogonal direction. Byconfiguring the detection unit to detect positions in both the conveyingdirection and the orthogonal direction as described above, the cost ofinstalling a device for performing position detection may be reduced. Inaddition, because the number of devices can be reduced, spaceconservation may be achieved, for example.

Referring back to FIG. 2, in the following descriptions, a sensorinstalled for the black liquid ejection head unit 210K is referred to as“black sensor SENK”. Similarly, a sensor installed for the cyan liquidejection head unit 210C is referred to as a “cyan sensor SENC”. Also, asensor installed for the magenta liquid ejection head unit 210M isreferred to as “magenta sensor SENM”. Further, a sensor installed forthe yellow liquid ejection head unit 210Y is referred to as “yellowsensor SENY”.

Note that in the example of FIG. 2, the black sensor SENK, the cyansensor SENC, the magenta sensor SENM, and the yellow sensor SENYcorrespond to examples of the first sensor (first detection unit). Also,the sensor SEN2 arranged upstream of the above first sensors correspondsto an example of the second sensor (second detection unit).

In the following descriptions, “sensor installation position” refers toa position where detection is performed. In other words, not all theelements of the detection unit have to be installed at each “sensorinstallation position”. For example, elements other than a sensor may beconnected by a cable and installed at some other position. Note that inFIG. 2, the black sensor SENK, the cyan sensor SENC, the magenta sensorSENM, and the yellow sensor SENY are installed at their correspondingsensor installation positions.

As illustrated, the installation positions of the first sensors for theliquid ejection head units are preferably located relatively close tothe corresponding landing positions of the liquid ejection head units.By arranging the first sensor close to each landing position, thedistance between each landing position and the first sensor may bereduced. By reducing the distance between each landing position and thefirst sensor, detection errors may be reduced. In this way, the imageforming apparatus 110 may be able to accurately detect a position of arecording medium, such as the web 120, in the orthogonal direction usingthe first sensors.

Specifically, the sensor installation position close to the landingposition may be located between the first roller and the second rollerof each liquid ejection heat unit. That is, in the example of FIG. 2,the installation position of the black sensor SENK is preferablysomewhere within range INTK1 between the first roller CR1K and thesecond roller CRK2. Similarly, the installation position of the cyansensor SENC is preferably somewhere within range INTC1 between the firstroller CR1C and the second roller CR2C. Also, the installation positionof the magenta sensor SENM is preferably somewhere within range INTM1between the first roller CR1M and the second roller CR2M. Further, theinstallation position of the yellow sensor SENY is preferably somewherewithin range INTY1 between the first roller CR1Y and the second rollerCY2Y.

By installing a sensor between each pair of rollers as described above,the sensor may be able to detect the position of a recording medium at aposition close to the landing position of each liquid ejection headunit. Note the moving speed of a conveyed object (e.g., recordingmedium) tends to be relatively stable between the pair of rollers. Thus,the image forming apparatus 110 may be able to accurately detect theposition of a conveyed object such as a recording medium in theorthogonal direction.

Moreover, the installation position of the first sensor is preferablylocated toward the first roller with respect to the landing positionbetween the pair of rollers. That is, as illustrated in FIG. 2, theinstallation position of the first sensor is preferably located upstreamof the landing position of each liquid ejection head unit.

Specifically, the installation position of the black sensor SENK ispreferably located upstream of the black landing position PK, betweenthe black landing position PK and the installation position of the firstroller CR1K (hereinafter referred to as “black upstream section INTK2”).Similarly, the installation position of the cyan sensor SENC ispreferably located upstream of the cyan landing position PC, between thecyan landing position PC and the installation position of the firstroller CR1C (hereinafter referred to as “cyan upstream section INTC2”).Also, the installation position of the magenta sensor SENM is preferablylocated upstream of the magenta landing position PM, between the magentalanding position PM and the installation position of the first rollerCR1M (hereinafter referred to as “magenta upstream section INTM2”).Further, the installation position of the yellow sensor SENY ispreferably located upstream of the yellow landing position PY, betweenthe yellow landing position PY and the installation position of thefirst roller CR1Y (hereinafter referred to as “yellow upstream sectionINTY2”).

By installing the first sensors within the black upstream section INTK2,the cyan upstream section INTC2, the magenta upstream section INTM2, andthe yellow upstream section INTY2, the image forming apparatus 110 maybe able to accurately detect a position of a recording medium in theorthogonal direction. Further, by installing the first sensors withinthe above sections, the first sensors may be positioned upstream of thelanding positions. In this way, the image forming apparatus 110 may beable to accurately detect a position of a recording medium in theorthogonal direction using the first sensor installed at the upstreamside of the landing position of each liquid ejection head unit andcalculate the ejection timing of each liquid ejection head unit. Thatis, for example, while performing the above calculation, the web 120 maybe conveyed toward the downstream side and each liquid ejection headunit may eject ink at the calculated timing.

Note that when the sensor installation position is located directlybelow each liquid ejection head unit, a color shift may occur due to adelay in control operations, for example. Thus, by arranging theinstallation position of the first sensor to be at the upstream side ofthe landing position of each liquid ejection head unit, the imageforming apparatus 110 may be able to reduce color shifts and improveimage quality, for example. Also, note that in some cases, theinstallation position of the first sensor may be restricted from beingtoo close to the landing position, for example. Thus, in someembodiments the installation position of the first sensor may be locatedtoward the first roller with respect to the landing position of eachliquid ejection head unit, for example.

Also, in some embodiments, the installation position of the first sensormay be arranged directly below each liquid ejection head unit (directlybelow the landing position of each liquid ejection head unit), forexample. In the following, an example case where the first sensor isinstalled directly below each liquid ejection head unit is described. Byinstalling the first sensor directly below each liquid ejection headunit, the first senor may be able to accurately detect an amount ofmovement directly below its installation position. Thus, if controloperations can be promptly performed, the first sensor is preferablylocated closer to a position directly below each liquid ejection headunit. Note, however, that the installation position of the first sensoris not limited to a position directly below each liquid ejection headunit, and even in such case, calculation operations similar to thosedescribed below may be implemented.

Also, in some embodiments, if errors can be tolerated, the installationposition of the first sensor may be located directly below each liquidejection head unit or at a position further downstream between the firstroller and the second roller, for example.

Note that in a case where the first sensors are arranged atsubstantially the same distances from each other, the second sensor mayalso be arranged at substantially the same distance from the closestfirst sensor. Specifically, with respect to the example of FIG. 2, thefirst sensors may be arranged such that the distance between the blacksensor SENK and the cyan sensor SENC, the distance between the cyansensor SENC and the magenta sensor SENM, and the distance between themagenta sensor SENM and the yellow sensor SENY are substantially thesame, for example. In such case the second sensor SEN2 is preferablyarranged such that the distance between the second sensor SEN2 and theblack sensor SENK may be substantially the same as the distance betweenthe black sensor SENK and the cyan sensor SENC. Note that the detectionaccuracy of the sensors is often calculated based on the distancebetween the sensors. Thus, by arranging the distance between the sensorsto be substantially the same, the detection accuracy of the sensors maybe substantially uniform, for example.

Also, the installation position of the second sensor is preferablylocated downstream of a roller around which the web may be wound. Thatis, when the web is wound around a roller, the web is prone topositional variations, for example. Thus, the second sensor ispreferably arranged to detect a position of the web after the web passessuch roller, i.e., at a downstream side of the roller. In this way, adetection result obtained by the second sensor may be less susceptibleto influences of positional variations of the web due to the web beingwound around the roller, for example. Note that in the example of FIG.2, the web 120 is prone to be wound around the roller 230 to form arelatively acute angle with respect to the roller 230 such that the web120 may be susceptible to positional variations at the roller 230. Thus,in the example of FIG. 2, the second sensor SEN2 is preferably arrangeddownstream of the roller 230.

Also, the image forming apparatus 110 may further include a measuringunit such as an encoder. In the following, an example where themeasuring unit is implemented by an encoder will be described. Morespecifically, the encoder may be installed with respect to a rotationalaxis of the roller 230, for example. In this way, the amount of movementof the web 120 in the conveying direction may be measured based on theamount of rotation of the roller 230, for example. By using themeasurement result obtained by the encoder together with the detectionresult obtained by the sensors, the image forming apparatus 110 may beable to more accurately eject liquid onto the web 120, for example.

FIGS. 9A and 9B are diagrams illustrating an example case wherevariations occur in the position of a recording medium in the orthogonaldirection. Specifically, an example case is described where the web 120is conveyed in the conveying direction 10 as illustrated in FIG. 9A. Asillustrated in this example, the web 120 is conveyed by rollers and thelike. When the web 120 is conveyed in this manner, variations may occurin the position of the web 120 in the orthogonal direction asillustrated in FIG. 9B, for example. That is, the web 120 may “meander”side to side in the orthogonal direction as illustrated in FIG. 9B.

In the illustrated example, the variations in the position of the web120 occur as a result of the slanting of the rollers (see FIG. 9A). Notethat although FIG. 9A illustrates a state where one of the rollers isconspicuously slanted for the sake of facilitating understanding, theslanting of the roller may be less conspicuous than the illustratedexample.

Variations in the position of the web 120 in the orthogonal direction,i.e., “meandering”, may occur as a result of eccentricity/misalignmentof the conveying rollers or from cutting the web 120 with a blade, forexample. Also, the “meandering” of the web 120 as illustrated in FIG. 9Bmay be caused by the physical shape of the web 120, such as when the web120 is not uniformly cut by the blade, for example.

FIG. 10 is a diagram illustrating an example cause of a color shift. Asdescribed above with reference to FIGS. 9A and 9B, when variations occurin the position of the recording medium in the orthogonal direction,i.e., when “meandering” occurs, a color shift is more likely to occur inthe manner illustrated in FIG. 10, for example.

Specifically, when forming an image on a recording medium using aplurality of colors, i.e., when forming a color image, the image formingapparatus 110 forms a so-called color plane on the web 120 bysuperimposing inks in the different colors that are ejected from theliquid ejection head units.

However, variations may occur in the position of the web 120 in theorthogonal direction as illustrated in FIGS. 9A and 9B. For example,“meandering” of the web 120 may occur with respect to a reference line320 as illustrated in FIG. 10. In such case, when the liquid ejectionhead units for the different colors eject ink at the same position withrespect to the orthogonal direction, the inks ejected on the web 120 maybe shifted from each other to create a color shift 330 due to the“meandering” of the web 120 in the orthogonal direction. That is, thecolor shift 330 occurs as a result of lines formed by the inks ejectedby the liquid ejection head units being shifted with respect to oneanother in the orthogonal direction. As described above, when the colorshift 330 occurs, the image quality of the image formed on the web 120may be degraded.

<Control Unit>

The controller 520 of FIG. 2, as an example of a control unit, may havea configuration as described below, for example.

FIG. 11 is a block diagram illustrating an example hardwareconfiguration of a control unit according to an embodiment of thepresent invention. For example, the controller 520 illustrated in FIG.11 includes a host apparatus 71, which may be an information processingapparatus, and a printer apparatus 72. In the illustrated example, thecontroller 520 causes the printer apparatus 72 to form an image on arecording medium based on image data and control data input by the hostapparatus 71.

The host apparatus 71 may be a PC (Personal Computer), for example. Theprinter apparatus 72 includes a printer controller 72C and a printerengine 72E.

The printer controller 72C controls the operation of the printer engine72E. The printer controller 72C transmits/receives control data to/fromthe host apparatus 71 via a control line 70LC. Also, the printercontroller 72C transmits/receives control data to/from the printerengine 72E via a control line 72LC. When various printing conditionsindicated by the control data are input to the printer controller 72C bysuch transmission/reception of control data, the printer controller 72Cstores the printing conditions using a register, for example. Then, theprinter controller 72C controls the printer engine 72E based on thecontrol data and forms an image based on print job data, i.e., thecontrol data.

The printer controller 72C includes a CPU (Central Processing Unit)72Cp, a print control device 72Cc, and a storage device 72Cm. The CPU72Cp and the print control device 72Cc are connected by a bus 72Cb tocommunicate with each other. Also, the bus 72Cb may be connected to thecontrol line 70LC via a communication I/F (interface), for example.

The CPU 72Cp controls the overall operation of the printer apparatus 72based on a control program, for example. That is, the CPU 72Cp mayimplement functions of a calculating device and a control device.

The print control device 72Cc transmits/receives data indicating acommand or a status, for example, to/from the printer engine 72E basedon the control data from the host apparatus 71. In this way, the printcontrol device 72Cc controls the printer engine 72E. Note that thestorage unit 110F3 of the detection unit as illustrated in FIG. 8 may beimplemented by the storage device 72Cm, for example. Also, the speedcalculating unit 110F4 may be implemented by the CPU 72Cp, for example.However, the storage unit 110F3 and the speed calculating unit 110F4 mayalso be implemented by some other calculating device and storage device.

The printer engine 72E is connected to a plurality of data lines 70LD-C,70LD-M, 70LD-Y, and 70LD-K. The printer engine 72E receives image datafrom the host apparatus 71 via the plurality of data lines. Then, theprinter engine 72E forms an image in each color under control by theprinter controller 72C.

The printer engine 72E includes a plurality of data management devices72EC, 72EM, 72EY, and 72EK. Also, the printer engine 72E includes animage output device 72Ei and a conveyance control device 72Ec.

FIG. 12 is a block diagram illustrating an example hardwareconfiguration of the data management device of the control unitaccording to an embodiment of the present invention. For example, theplurality of data management devices 72EC, 72EM, 72EY, and 72EK may havethe same configuration. In the following, it is assumed that the datamanagement devices 72EC, 72EM, 72EY, and 72EK have the sameconfiguration, and the configuration of the data management apparatus72EC is described as an example. Thus, overlapping descriptions will beomitted.

The data management device 72EC includes a logic circuit 72EC1 and astorage device 72ECm. As illustrated in FIG. 12, the logic circuit 72EC1is connected to the host apparatus 71 via a data line 70LD-C. Also, thelogic circuit 72EC1 is connected to the print control device 72Cc viathe control line 72LC. Note that the logic circuit 72EC1 may beimplemented by an ASIC (Application Specific Integrated Circuit) or aPLD (Programmable Logic Device), for example.

Based on a control signal input from the printer controller 72C (FIG.11), the logic circuit 72EC1 stores image data input by the hostapparatus 71 in the storage device 72ECm.

Also, the logic circuit 72EC1 reads cyan image data Ic from the storagedevice 72ECm based on the control signal input from the printercontroller 72C. Then, the logic circuit 72EC1 sends the read cyan imagedata Ic to the image output device 72Ei.

Note that the storage device 72ECm preferably has a storage capacity forstoring image data of about three pages or more, for example. Byconfiguring the storage device 72ECm to have a storage capacity forstoring image data of about three pages or more, the storage device72ECm may be able to store image data input by the host apparatus 71,image data of an image being formed, and image data for forming a nextimage, for example.

FIG. 13 is a block diagram illustrating an example hardwareconfiguration of the image output device 72Ei included in the controlunit according to an embodiment of the present invention. As illustratedin FIG. 13, the image output device 72Ei includes an output controldevice 72Eic and the plurality of liquid ejection head units, includingthe black liquid ejection head unit 210K, the cyan liquid ejection headunit 210C, the magenta liquid ejection head unit 210M, and the yellowliquid ejection head unit 210Y.

The output control device 72Eic outputs image data of each color to thecorresponding liquid ejection head unit for the corresponding color.That is, the output control device 72Eic controls the liquid ejectionhead units for the different colors based on image data input thereto.

Note that the output control device 72Eic may control the plurality ofliquid ejection head units simultaneously or individually. That is, forexample, upon receiving a timing input, the output control device 72Eicmay perform timing control for changing the ejection timing of liquid tobe ejected by each liquid ejection head unit. Note that the outputcontrol device 72Eic may control one or more of the liquid ejection headunits based on a control signal input by the printer controller 72C(FIG. 11), for example. Also, the output control device 72Eic maycontrol one or more of the liquid ejection head units based on anoperation input by a user, for example.

Note that the printer apparatus 72 illustrated in FIG. 11 is an exampleprinter apparatus having two distinct paths including one path forinputting image data from the host apparatus 71 and another path usedfor transmission/reception of data between the host apparatus 71 and theprinter apparatus 72 based on control data.

Also, note that the printer apparatus 72 may be configured to form animage using one color, such as black, for example. In the case where theprinter apparatus 72 is configured to form an image with only black, forexample, the printer engine 72E may include one data management deviceand four black liquid ejection head units in order to increase imageforming speed, for example.

The conveyance control device 72Ec (FIG. 11) may include a motor, amechanism, and a driver device for conveying the web 120. For example,the conveyance control device 72Ec may control a motor connected to eachroller to convey the web 120.

<Overall Process>

FIG. 14 is a flowchart illustrating an example overall processimplemented by the liquid ejection apparatus according to an embodimentof the present invention. For example, in the process described below,it is assumed that image data representing an image to be formed on theweb 120 (FIG. 1) is input to the image forming apparatus 110 in advance.Then, based on the input image data, the image forming apparatus 110 mayperform the process as illustrated in FIG. 14 to form the imagerepresented by the image data on the web 120.

Note that FIG. 14 illustrates a process that is implemented for oneliquid ejection head unit. For example, the process of FIG. 14 mayrepresent a process implemented with respect to the black liquidejection head unit 210K of FIG. 2. The process of FIG. 14 may beseparately implemented for the other liquid ejection head units for theother colors in parallel or before/after the process of FIG. 14 that isimplemented with respect to the black liquid ejection head unit 210K.

In step S01, the image forming apparatus 110 calculates an amount ofpositional variation of a recording medium based on a plurality of setsof sensor data. That is, in step S01, the image forming apparatus 110detects a position of a recording medium in the orthogonal directionusing each of the plurality of sensors. Then, the image formingapparatus 110 acquires sensor data indicating a detection result outputby each of the plurality of sensors. Then, the image forming apparatus110 calculates the amount of positional variation of the recordingmedium based on the plurality of detection results (sensor data) outputby the plurality of sensors. Note that a calculation method used tocalculate the amount of positional variation is described in detailbelow.

In step S02, the image forming apparatus 110 moves the liquid ejectionhead unit in the orthogonal direction that is orthogonal to theconveying direction of the recording medium. Note that the process ofstep S02 is implemented based on the detection results obtained in stepS01. Further, in step S02, the liquid ejection head unit is moved tocompensate for the variation in the position of the recording mediumthat is indicated by the detection results obtained in step S01. Forexample, in step S02, the image forming apparatus 110 may compensate forthe positional variation of the web 120 by moving the liquid ejectionhead unit by an amount corresponding to the amount of positionalvariation of the web 120 in the orthogonal direction detected in stepS01.

FIG. 15 is a block diagram illustrating an example hardwareconfiguration for moving the liquid ejection head units based on theamount of positional variation of a recording medium according to anembodiment of the present invention. In the illustrated example of FIG.15, the image forming apparatus 110 includes a plurality of actuatorsAC1 to AC4 and the plurality of sensors SEN2, SENK, SENC, SENM, andSENY. Also, the image forming apparatus 110 includes a speed detectioncircuit SCR. Further, in FIG. 15, the image forming apparatus 110 isconnected to a control device CTRL. The control device CTRL includes aCPU 221, a ROM (Read-Only Memory) 222, and a RAM (Random Access Memory)223. Also, as illustrated in FIG. 15, the image forming apparatus 110may include a plurality of I/O (input/output) interfaces fortransmitting/receiving data to/from the plurality of actuators, sensors,and other devices.

Note that the above configuration is merely one example configurationfor implementing the above-described process. That is, the devicesillustrated in FIG. 15 may be included in the image forming apparatus110 or provided as external devices, for example.

Also, the devices illustrated in FIG. 15 may be configured to implementfunctions of other devices. For example, the CPU 221 may also act as aCPU for implementing the detection unit, or a separate CPU may beprovided for implementing the detection unit.

The CPU 221 is an example of a calculating device and a control device.Specifically, the CPU 221 acquires the detection results of therespective sensors and performs calculation operations for calculatingthe amount of positional variation of a conveyed object. Further, theCPU 221 controls the actuators to move the liquid ejection head units.

The ROM 222 and the RAM 223 are examples of storage devices. Forexample, the ROM 222 stores programs and data to be used by the CPU 221.Further, the RAM 223 acts as a storage area that stores a program usedby the CPU 22 to perform calculation operations, for example.

The speed detection circuit SCR is an electronic circuit for detectingthe moving speed of a conveyed object. For example, a “6-ppi (pixels perinch)” signal may be input to the speed detection circuit SCR. In turn,the speed detection circuit SCR may calculate the speed at which theconveyed object is conveyed based on the detection result from eachsensor or a detection result from an encoder, for example, and transmitthe calculated speed to the CPU 221. Note that the speed detectioncircuit SCR may be the same as or different from the FPGA of FIG. 4.

Each of the actuators AC1-AC4 is connected to the corresponding liquidejection head unit that is to be moved by the actuator. Specifically,the first actuator AC1 is connected to the black liquid ejection headunit 210K. That is, the first actuator AC1 moves the black liquidejection head unit 210K in the orthogonal direction. Similarly, thesecond actuator AC2 is connected to the cyan liquid ejection head unit210C. That is, the second actuator AC2 moves the cyan liquid ejectionhead unit 210C in the orthogonal direction orthogonal to the conveyingdirection of the web. Further, the third actuator AC3 is connected tothe magenta liquid ejection head unit 210 M. That is, the third actuatorAC3 moves the magenta liquid ejection head unit 210M in the orthogonaldirection. Further, the fourth actuator AC4 is connected to the yellowliquid ejection head unit 210Y. That is, the fourth actuator AC4 movesthe yellow liquid ejection head unit 210Y in the orthogonal direction.

Note that each of the actuators AC1-AC4 may move the correspondingliquid ejection head unit using the following moving mechanism, forexample.

FIG. 16 is a block diagram illustrating an example moving mechanism formoving a liquid ejection head unit of the liquid ejection apparatusaccording to an embodiment of the present invention. The movingmechanism may have a hardware configuration as illustrated in FIG. 16,for example. Note that the example hardware configuration illustrated inFIG. 16 is for moving the cyan liquid ejection head unit 210C.

In the illustrated example of FIG. 16, an actuator ACT such as a linearactuator for moving the cyan liquid ejection head unit 210C is installedin the cyan liquid ejection head unit 210C. Further, the controller CTLfor controlling the actuator ACT is connected to the actuator ACT.

The actuator ACT may be a linear actuator or a motor, for example. Also,the actuator ACT may include a control circuit, a power supply circuit,and mechanical components, for example.

The controller CTL receives a detection result obtained in step S01 ofFIG. 14 as an input. In turn, the controller CTL controls the actuatorACT to move the cyan liquid ejection head unit 210C to compensate forthe variation in the position of the web 120 indicated by the detectionresult (step S02 of FIG. 12).

In the illustrated example of FIG. 13, the detection result input to thecontroller CTL may indicate a variation Δ, for example. Thus, in thepresent example, the controller CTL may control the actuator ACT to movethe cyan liquid ejection head unit 210C in the orthogonal direction 20to compensate for the variation Δ.

Note that the hardware configuration of the controller 520 illustratedin FIG. 12 and the hardware configuration for moving a liquid ejectionhead unit as illustrated in FIG. 13 may be integrated or they may beseparate.

Referring back to FIG. 15, the control device CTRL receives thedetection result output by each sensor. Specifically, the control deviceCTRL is connected to the second sensor SEN2. Also, the control deviceCTRL is connected to the first sensors SEN1. Note that in theillustrated example, the first sensors SEN1 include the black sensorSENK, the cyan sensor SENC, the magenta sensor SENM, and the yellowsensor SENY.

FIG. 17 is a timing chart illustrating an example method of calculatinga variation in the position of a recording medium that may beimplemented by the liquid ejection apparatus according to an embodimentof the present invention. As illustrated in FIG. 17, the control deviceCTRL (FIG. 15) calculates the amount of positional variation of arecording medium based on a plurality of detection results.Specifically, based on a first detection result S1 and a seconddetection result S2, the control device CTRL outputs a calculationresult indicating an amount of positional variation of a recordingmedium. Note that the first detection result S1 and the second detectionresult S2 may be detection results indicated by sensor data output byany two sensors selected from the group consisting of the first sensorsSEN1 and the second sensor SEN2 illustrated in FIG. 15, for example. Thesensor data output by the sensors are transmitted to the control deviceCTRL and stored as detection results in the RAM 223. Thus, the controldevice CTRL calculates the amount of positional variation of therecording medium based on the plurality of detection results indicatedby the stored sensor data.

Note that the amount of positional variation may be calculated withrespect to each liquid ejection head unit. In the following, an examplecase of calculating the amount of positional variation for the cyanliquid ejection head unit 210C (FIG. 2) is described. In the presentexample, the amount of positional variation may be calculated based on adetection result output by the cyan sensor SENC (FIG. 2) and a detectionresult output by the black sensor SENK (FIG. 2), which is installed oneplace upstream (immediately upstream) of the cyan sensor SENC, forexample. In FIG. 17, it is assumed that the first detection result S1corresponds to the detection result output by the black sensor SENK andthe second detection result S2 corresponds to the detection resultoutput by the cyan sensor SENC.

Also, in the present example, assuming “L2” represents the distancebetween the black sensor SENK and the cyan sensor SENC, “V” representsthe moving speed detected by the speed detection circuit SCR, and “T2”represents a moving time that is required for moving a conveyed object(e.g., recording medium) from the position of the black sensor SENK tothe position of the cyan sensor SENC, the moving time may be calculatedas follows.

T2=L2/V

Also, assuming “A” represents a sampling period and “n” represents thesampling frequency of the black sensor SENK and the cyan sensor SENC,the sampling frequency “n” may be calculated as follows.

n=T2/A

Also, in the present example, it is assumed that the “ΔX” represents thecalculation result, i.e., the amount of positional variation. Forexample, with respect to a detection cycle “0” as the current detectioncycle, the amount of positional variation “ΔX” may be calculated bycomparing the first detection result S1 that was obtained a time periodof “T2” earlier and the second detection result S2 obtained at thedetection cycle “0”. Specifically, the amount of positional variation“ΔX” may be calculated as follows.

ΔX=X2(0)−X1(n)

Note that in the case where the sensor is installed closer to the firstroller than the landing position of the liquid ejection head unit, thecontrol device CTRL may calculate the amount of positional variation ofa recording medium at the time the recording medium has moved to theposition of the sensor and drive the actuators based on the calculatedamount of positional variation.

After calculating the variation “ΔX”, the control device CTRL controlsthe second actuator AC2 (FIG. 15) to move the cyan liquid ejection headunit 210C (FIG. 16) in the orthogonal direction to compensate for thevariation “ΔX”. In this way, even when the position of a conveyed objectvaries in the orthogonal direction, the image forming apparatus 110 maybe able to accurately form an image on the conveyed object, for example.Also, by calculating the variation based on two detection results outputby two sensors, the variation may be calculated without integrating theposition information of each of the sensors, for example. In this way,accumulation of detection errors by the sensors may be reduced, forexample.

Note that the above calculation method for calculating the variation maysimilarly be implemented with respect to the other liquid ejection headunits. For example, the variation for the black liquid ejection headunit 210K (FIG. 2) may be calculated based on a first detection resultS1 corresponding to a detection result output by the second sensor SEN2and a second detection result S2 corresponding to a detection resultoutput by the black sensor SENK. Similarly, the variation for themagenta liquid ejection head unit 210M (FIG. 2) may be calculated basedon a first detection result S1 corresponding to a detection resultoutput by the cyan sensor SENC and a second detection result S2corresponding to a detection result output by the magenta sensor SENM.Further, the variation for the yellow liquid ejection head unit 210Y(FIG. 2) may be calculated based on a first detection result S1corresponding to a detection result output by the magenta sensor SENMand a second detection result S2 corresponding to a detection resultoutput by the yellow sensor SENY.

Also, note that the first detection result S1 is not limited to adetection result output by the sensor installed one place upstream(immediately upstream) of the sensor provided for the liquid ejectionhead unit to be moved. That is, the first detection result S1 may be adetection result output by any sensor that is located upstream of theliquid ejection head unit to be moved. For example, when calculating thevariation for the yellow liquid ejection head unit 210Y, the firstdetection result S1 may be a detection result output by the secondsensor SEN2, the black sensor SENK, the cyan sensor SENC, or the magentasensor SENM.

On the other hand, the second detection result S2 preferably correspondsto a detection result output by the sensor that is closest to the liquidejection head unit to be moved.

Further, note that in some embodiments, the variation may be detectedbased on three or more detection results, for example.

By moving a liquid ejection head unit based on a variation calculatedfrom a plurality of detection results output by a plurality of sensorswhen ejecting liquid onto a recording medium, an image may be accuratelyformed on the recording medium, for example.

<Processing Result>

FIG. 18 is a diagram illustrating an example test pattern used by theliquid ejection apparatus according to an embodiment of the presentinvention. In the present example, the image forming apparatus 110performs test printing by forming a straight line in the conveyingdirection 10 using black as an example of a first color. A distance Lkfrom an edge may be obtained based on the result of the test printing.By adjusting the distance Lk from the edge in the orthogonal direction,manually or using a device, the landing position of black inkcorresponding to the first color to be used as a reference may bedetermined.

Also, note that the installation position of the first sensor ispreferably located closer to the first roller than the landing position.

FIG. 19 is a diagram illustrating an example installation position of afirst sensor of the liquid ejection apparatus according to an embodimentof the present invention. In the following, the installation position ofthe black sensor SENK is described as an example. The black sensor SENK,which is located between the first roller CR1K and the second rollerCR2K, is preferably located closer to the first roller CR1K than theblack landing position PK. Note that the shifting distance of theinstallation position of the black sensor SENK toward the first rollerCR1K with respect to the black landing position PK may be determinedbased on the requisite time for performing control operations and thelike. For example, the shifting distance toward the first roller CR1Kmay be set to “20 mm”. In this case, the installation position of theblack sensor SENK would be located “20 mm” upstream of the black landingposition PK.

In the present example, the black sensor SENK detects a position POS ofthe web 120 with respect to the orthogonal direction. For example, theposition POS correspond to an edge portion of the web 120. Note,however, that the position POS of the web 120 is not limited to aposition at the edge portion of the web 120 and may be a position atsome other portion of the web 120. As illustrated in FIG. 19, theinstallation position of the black sensor SENK is not the same as theblack landing position PK but is shifted upstream of the black landingposition PK. In such case, a detection error E1 is created between theposition POS of the web 120 detected by the black sensor PK and aposition of the web 120 corresponding to the black landing position PK.As the distance between the installation position of the black sensorSENK and the black landing position PK is reduced, the detection errorE1 can be reduced.

Thus, by arranging the installation position of the first sensor to berelatively close to the landing position, the detection error E1 may becontrolled to be relatively small. Further, by controlling the detectionerror E1 to be relatively small, the image forming apparatus 110 may beable to accurately control the landing positions of the liquids in thedifferent colors. Thus, when forming an image, liquids in the differentcolors may be controlled to land with high accuracy such that the imageforming apparatus 110 may be able to reduce color shifts and improve theimage quality of the formed image, for example.

Also, with such a configuration, the image forming apparatus 110 may befree from design restrictions, such as a requirement that the distancebetween the liquid ejection head units be an integer multiple of acircumference of the roller 230 (FIG. 2), for example. As such, theinstallation positions of the liquid ejection head units may be morefreely determined, for example. That is, even when the distance betweenthe liquid ejection head units is not an integer multiple of thecircumference of the roller 230, the image forming apparatus 110 maystill be able to accurately control the landing positions of liquids inthe different colors that are ejected by the liquid ejection head units,for example.

Comparative Example

FIG. 20 is a diagram illustrating an example hardware configurationaccording to a first comparative example. In the illustrated firstcomparative example, a position of the web 120 is detected before eachliquid ejection head unit reaches its corresponding liquid landingposition. For example, in the first comparative example, theinstallation positions of the sensors SENK, SENC, SENM, and SENY mayrespectively be located “200 mm” upstream of the position directly belowtheir corresponding liquid ejection head units 210K, 210C, 210M, and210Y. Based on detection results obtained by the sensors in this case,the image forming apparatus 110 according to the first comparativeexample may move the liquid ejection head units to compensate for thevariations in the position of the web 120.

FIG. 21 is a diagram illustrating an example processing result of anoverall process implemented by the liquid ejection apparatus accordingto the first comparative example. In the first comparative example, theliquid ejection head units are installed so that the distance betweenthe liquid ejection head units is an integer multiple of thecircumference d of the roller 230. In this case, the difference betweenthe position of the web 120 detected by each sensor and the position ofthe web directly below each liquid ejection head unit can be controlledto be “0”. Thus, in the first comparative example, provided therespective distances from the web edge of the landing positions of theblack, cyan, magenta, and yellow inks on the web 120 are denoted as“Lk1”, “Lc1”, “Lm1”, and “Ly1”, a relationship “Lk1=Lc1=Lm1=Ly1” may beestablished. In this way, positional variations may be corrected in thefirst comparative example.

FIG. 22 is a diagram illustrating an example processing result of anoverall process implemented by the liquid ejection apparatus accordingto a second comparative example. Note that the second comparativeexample uses the same hardware configuration as that of the firstcomparative example. The second comparative example differs from thefirst comparative example in that the distance between the black liquidejection head unit 210K and the cyan liquid ejection head unit 210C andthe distance between the magenta liquid ejection head unit 210M and theyellow liquid ejection head unit 210Y are arranged to be “1.75d”. Thatis, in the second comparative example, the distance between the blackliquid ejection head unit 210K and the cyan liquid ejection head unit210C and the distance between the magenta liquid ejection head unit 210Mand the yellow liquid ejection head unit 210Y are not integer multiplesof the circumference d of the roller 230.

In the second comparative example illustrated in FIG. 22, the differencebetween a position of the web 120 detected by the black sensor SENK andthe position of the web 120 below the black liquid ejection head unit210K is denoted as “Pk”. Similarly, the difference between a position ofthe web 120 detected by the cyan sensor SENC and the position of the web120 below the cyan liquid ejection head unit 210C is denoted as “Pc”.Also, the difference between a position of the web 120 detected by themagenta sensor SENM and the position of the web 120 below the magentaliquid ejection head unit 210M is denoted as “Pm”. Further, thedifference between a position of the web 120 detected by the yellowsensor SENY and the position of the web 120 below the yellow liquidejection head unit 210Y is denoted as “Py”. Also, provided therespective distances from the web edge of the landing positions of theblack, cyan, magenta, and yellow inks on the web 120 are denoted as“Lk2”, “Lc2”, “Lm2”, and “Ly2”, the relationship between the respectivedistances may be represented by the following equations (2).

Lc2=Lk2−Pc

Lm2=Lk2

Ly2=Lk2−Py  (2)

Based on the above, “Lk2=Lm2≠Lc2=Ly2”. That is, in the secondcomparative example where the distance between the liquid ejection headunits 210K and 210C and the distance between the liquid ejection headunits 210M and 210Y are not integer multiples of the circumference d ofthe roller 230, the position of the web 120 directly below the cyanliquid ejection head unit 210C and the position of the web 120 directlybelow the yellow liquid ejection head unit 210Y are respectively shiftedfrom the position of the web 120 detected by the cyan sensor SENC andthe position of the web 120 detected by the yellow sensor SENY by shiftamounts “Pc” and “Py” that are not equal to zero. That is, in the secondcomparative example, variations in the position of the web 120 cannot becorrected such that color shifts may be more likely to occur, forexample.

FIG. 23 is a diagram illustrating an example sensor installationposition of a liquid ejection apparatus according to a third comparativeexample. As illustrated in FIG. 23, in the third comparative example,the black sensor SENK is installed at a position relatively far from theblack landing position PK as compared with the sensor installationposition illustrated in FIG. 19, for example. In such case, a detectionerror E2 tends to increase such that the landing positions of liquids inthe different colors may not be as accurately controlled as desired, forexample.

<Functional Configuration of Liquid Ejection Apparatus>

FIG. 24 is a block diagram illustrating an example functionalconfiguration of the liquid ejection apparatus according to anembodiment of the present invention. In FIG. 24, the image formingapparatus 110 includes a plurality of liquid ejection head units and adetection unit 110F10 for each of the liquid ejection head units. Also,the image forming apparatus 110 includes a movement control unit 110F20.Further, the image forming apparatus 110 includes a calculating unit110F30 that is provided for each of the liquid ejection head units.

The plurality of liquid ejection head units are arranged at differentpositions along a conveying path for a conveyed object as illustrated inFIG. 2, for example. In the following, the black liquid ejection headunit 210K of FIG. 2 is described as an example liquid ejection head unitof the plurality of liquid ejection head units.

Also, as illustrated in FIG. 24, the image forming apparatus 110 of thepresent embodiment preferably includes a measuring unit 110F40.

In FIG. 24, the detection unit 110F10 is provided for each of the liquidejection head units. Specifically, in the image forming apparatus 110having the configuration as illustrated in FIG. 2, for example, fourdetection units 110F10 are provided for the four liquid ejection headunits 210K, 210C, 210M, and 210Y. The detection units 110F10 providedfor the respective liquid ejection head units are referred to as firstdetection units 110F101. In addition, a detection unit 110F10 providedupstream of the first detection units 110F101 is referred to as seconddetection unit 110F102. Each of the above detection units 110F10 detectsa position of the web 120 (recording medium) in the orthogonaldirection. Note that each of the detection units 110F10 may beimplemented by the hardware configuration as illustrated in FIG. 4, forexample. Also, note that each of the first detection units 110F101 andthe second detection unit 110F102 includes at least one detection unit110F10.

In the present embodiment, the first roller is provided for each liquidejection head unit. Specifically, in the image forming apparatus 110having the configuration as illustrated in FIG. 2, the number of thefirst rollers would be the same as the number of the liquid ejectionhead units, i.e., four. The first roller is a roller used to convey arecording medium (e.g., web 120) to a landing position such that aliquid ejection head unit may be able to eject liquid onto apredetermined position of the recording medium. That is, the firstroller is a roller installed upstream of the landing position. Forexample, the first roller CR1K is provided for the black liquid ejectionhead unit 210K (see FIG. 2).

The second roller is provided for each liquid ejection head unit.Specifically, in the image forming apparatus 110 having theconfiguration as illustrated in FIG. 2, the number of second rollerswould be the same as the number of liquid discharge head units, i.e.,four. The second roller is a roller used for conveying the recordingmedium from the landing position to another position. That is, thesecond roller is a roller installed downstream of the landing position.For example, the second roller CR2K is provided for the black liquidejection head unit 210K (see FIG. 2).

The calculating unit 110F30 calculates an amount of positional variationby comparing a plurality of detection results. For example, thecalculating unit 110F30 may calculate an amount of positional variationby implementing the calculation method as illustrated in FIG. 17. Notethat the calculating unit 110F30 may be implemented by the CPU 221 ofFIG. 15, for example.

The movement control unit 110F20 moves the liquid ejection head unitsbased on the detection results obtained by the plurality of detectionunits 110F10. For example, the movement control unit 110F20 may move theliquid ejection head units to compensate for the variations calculatedby the calculating units 110F30. Note that the movement control unit110F20 may be implemented by the hardware configuration and the movingmechanism as illustrated in FIGS. 15 and 16, for example. Also, notethat the movement control unit 110F20 may be configured to control aplurality of liquid ejection heads as in the illustrated example.Alternatively, the movement control unit 110F20 may be separatelyprovided for each of the liquid ejection head units, for example.

By configuring the movement control unit 110F20 to move the liquidejection head units based on a plurality of detection results obtainedby a plurality of detection units 110F10, the image forming apparatus110 may be able to more accurately control the landing positions of theejected liquids in the orthogonal direction, for example.

Also, the position at which the first detection unit 110F101 performsdetection, i.e., the installation position of the first sensor, ispreferably located close to the landing position. For example, theinstallation position of the black sensor SENK is preferably close tothe black landing position PK, such as somewhere within the range INTK1between the first roller CR1K and the second roller CR2K. That is, whendetection is performed at a position within the range INTK1, forexample, the image forming apparatus 110 may be able to accuratelydetect a position of a recording medium in the orthogonal direction.

Further, the position at which the first detection unit 110F10 performsdetection, i.e., the installation position of the first sensor, ispreferably located upstream of the landing position. For example, theinstallation position of the black sensor SENK is preferably locatedupstream of the black landing position PK, such as somewhere within theblack upstream section INTK2, between the first roller CR1K and thesecond roller CR2K. When detection is performed at a position within theblack upstream section INTK2, for example, the image forming apparatus110 may be able to accurately detect a position of a recording medium inthe orthogonal direction.

As described above, in a liquid ejection apparatus according to anembodiment of the present invention, a position of a conveyed object,such as a recording medium, in the orthogonal direction is detected ateach of a plurality of liquid ejection head units at a detectionposition close to each of the liquid ejection head units. Also, theliquid ejection apparatus according to an embodiment of the presentinvention detects a position of the conveyed object at the upstream sideof a liquid ejection head unit to be moved. The combination of detectionresults to be used may vary depending on the liquid ejection head unitto be moved. For example, a combination of a detection result obtainedby the detection unit 110F10 located closest to the liquid ejection headunit to be moved and a detection result obtained by a detection unit110F10 installed one place upstream (immediately upstream) of theclosest detection unit 110F10 may be used to calculate an amount ofpositional variation of the conveyed object. In this case, a firstcombination RES1, a second combination RES2, a third combination RES3,and a fourth combination RES4 of detection results as illustrated inFIG. 24 may be used to calculate the amounts of positional variation forthe respective liquid ejection head units. That is, the calculatingunits 110F30 for the respective liquid ejection head units may calculatethe amounts of positional variation for the respective liquid ejectionhead units based on the first combination RES1, the second combinationRES2, the third combination RES3, and the fourth combination RES4, forexample. By calculating the amounts of positional variation for therespective liquid ejection head units based on the above combinations ofdetection results, for example, accuracy of the calculated amounts ofpositional variation may be uniform.

Note that when a position of a conveyed object is detected using asingle detection unit, a detection range subject to detection may berelatively small. As such, an amount of positional variation calculatedusing a detection result obtained by one single detection unit may notbe as accurate as desired. On the other hand, by calculating an amountof positional variation based on a combination of detection resultsobtained by a plurality of detection units as in the present embodiment,the amount of positional variation may be more accurately calculated ascompared to a case where the amount of positional variation iscalculated based on a detection result obtained by a single detectionunit. Also, by combining a plurality of detection results of a pluralityof detection units, an amount of positional variation of a conveyedobject occurring between the sensors, and an amount of positionalvariation of the conveyed object occurring between the sensor and theliquid ejection head unit may be calculated, for example. That is, bycombining a plurality of detection results obtained by a plurality ofdetection units as in the present embodiment, the liquid ejectionapparatus may be able to accurately compensate for the positionalvariations.

Then, based on the amounts of variation calculated for the respectiveliquid ejection head units using the combinations of detection results,the liquid ejection apparatus according to an embodiment of the presentinvention moves the liquid ejection head units. In this way, the liquidejection apparatus according to an embodiment of the present inventionmay be able to accurately correct deviations in the landing positions ofejected liquid in the orthogonal direction as compared with the firstcomparative example and the second comparative example as illustrated inFIGS. 21 and 22, for example.

Also, in the liquid ejection apparatus according to an embodiment of thepresent invention, the distance between the liquid ejection head unitsdoes not have to be an integer multiple of the circumference of a rolleras in the first comparative example (FIG. 21), and as such, restrictionsfor installing the liquid ejection head units may be reduced.

Further, in the case of forming an image on a recording medium byejecting liquid, by improving the accuracy of the landing positions ofejected liquids in the different colors, the liquid ejection apparatusaccording to an embodiment of the present invention may be able toimprove the image quality of the formed image.

Also, by providing the measuring unit 110F40, the position of arecording medium such as the web 120 may be more accurately detected.For example, a measuring device such as an encoder may be installed withrespect to the rotational axis of the roller 230. In such case, themeasuring unit 110F30 may measure the amount of movement of therecording medium using the encoder. When such measurement obtained bythe measuring unit 110F40 is input, the image forming apparatus 110 maybe able to more accurately detect a position of a recording medium inthe conveying direction, for example.

<Modifications>

Note that in some embodiments, the installation position of the firstsensor may be located directly below the landing position of each liquidejection head unit, for example. By arranging the first sensor directlybelow the landing position, an amount of movement of a position directlybelow the sensor may be accurately detected by the first sensor. Thus,in a case where calculation of the amount of movement can be accuratelyexecuted, the sensor is preferably arranged close to a position directlybelow the landing position of the liquid ejection head unit. On theother hand, the sensor does not have to be arranged directly below eachliquid ejection head unit, and even in such case, similar calculationoperations may be performed.

Also, note that the liquid ejection apparatus according to an embodimentof the present invention may be implemented by a liquid ejection systemincluding at least one liquid ejection apparatus. For example, in someembodiments, the black liquid ejection head unit 210K and the cyanliquid ejection head unit 210C may be included in one housing of oneliquid ejection apparatus, and the magenta liquid ejection head unit210M and the yellow liquid ejection head unit 210Y may be included inanother housing of another liquid ejection apparatus, and the liquidejection apparatus according to an embodiment of the present inventionmay be implemented by a liquid ejection system including both of theabove liquid ejection apparatuses.

Also, note that the liquid ejected by the liquid ejection apparatus andthe liquid ejection system according to embodiments of the presentinvention is not limited to ink but may be other types of recordingliquid or fixing agent, for example. That is, the liquid ejectionapparatus and the liquid ejection system according to embodiments of thepresent invention may also be implemented in applications that areconfigured to eject liquid other than ink.

Also, the liquid ejection apparatus and the liquid ejection systemaccording to embodiments of the present invention are not limited toapplications for forming a two-dimensional image. For example,embodiments of the present invention may also be implemented inapplications for forming a three-dimensional object.

Also, in some embodiments, one member may be arranged to act as both thefirst support member and the second support member. For example, thefirst support member and the second support member may be configured asfollows.

FIG. 25 is a schematic diagram illustrating an example modifiedconfiguration of the liquid ejection apparatus according to anembodiment of the present invention. In the liquid ejection apparatusillustrated in FIG. 25, the configuration of the first support memberand the second support member differs from that illustrated in FIG. 2.Specifically, in FIG. 25, a first member RL1, a second member RL2, athird member RL3, a fourth member RL4, and a fifth member RL5 arearranged as the first support member and the second support member. Thatis, in FIG. 25, the second member RL2 acts as the second support memberfor the black liquid ejection head unit 210K and the first supportmember for the cyan liquid ejection head unit 210C. Similarly, the thirdmember RL3 acts as the second support member for the cyan liquidejection head unit 210C and the first support member for the magentaliquid ejection head unit 210M. Further, the fourth member RL4 acts asthe second support member for the magenta liquid ejection head unit 210Mand the first support member for the yellow liquid ejection head unit210Y. As illustrated in FIG. 25, in some embodiments, one support membermay be configured to act as the second support member of an upstreamliquid ejection head unit and the first support member of a downstreamliquid ejection head unit, for example. Also, in some embodiments, aroller or a curved plate may be used as the support member acting asboth the first support member and the second support member, forexample.

Further, the conveyed object is not limited to recording medium such aspaper. That is, the conveyed object may be any material onto whichliquid can be ejected including paper, thread, fiber, cloth, leather,metal, plastic, glass, wood, ceramic materials, and combinationsthereof, for example.

Also, embodiments of the present invention may be implemented by acomputer program that causes a computer of an image forming apparatusand/or an information processing apparatus to execute a part or all of aliquid ejection method according to an embodiment of the presentinvention, for example.

Although the present invention has been described above with referenceto certain illustrative embodiments, the present invention is notlimited to these embodiments, and numerous variations and modificationsmay be made without departing from the scope of the present invention.

What is claimed is:
 1. A liquid ejection apparatus, comprising: aplurality of liquid ejection head units that are configured to ejectliquid onto a conveyed object at different positions along a conveyingpath for conveying the conveyed object; a first support member thatsupports the conveyed object and is provided upstream of a landingposition of the liquid ejected onto the conveyed object by acorresponding liquid ejection head unit of the plurality of liquidejection head units; a second support member that supports the conveyedobject and is provided downstream of the landing position of thecorresponding liquid ejection head unit; at least one first detectionunit that is installed between the first support member and the secondsupport member and is configured to detect a position of the conveyedobject with respect to an orthogonal direction that is orthogonal to aconveying direction of the conveyed object; at least one seconddetection unit that is installed upstream of the first detection unitand is configured to detect the position of the conveyed object withrespect to the orthogonal direction; and a movement control unit that isconfigured to move each liquid ejection head unit of the plurality ofliquid ejection head units based on at least two detection resultsselected from a plurality of detection results output by the firstdetection unit and the second detection unit.
 2. The liquid ejectionapparatus according to claim 1, wherein the first support member isarranged downstream of a landing position of an upstream liquid ejectionhead unit located upstream of the corresponding liquid ejection headunit; and the second support member is arranged upstream of a landingposition of a downstream liquid ejection head unit located downstream ofthe corresponding liquid ejection head unit.
 3. The liquid ejectionapparatus according to claim 1, wherein the first support member and thesecond support member are provided with respect to the each liquidejection head unit of the plurality of liquid ejection head units. 4.The liquid ejection apparatus according to claim 1, wherein the firstdetection unit is positioned between the first support member and thelanding position of the corresponding liquid ejection head unit.
 5. Theliquid ejection apparatus according to claim 1, wherein the movementcontrol unit moves the each liquid ejection head unit in the orthogonaldirection that is orthogonal to the conveying direction of the conveyedobject.
 6. The liquid ejection apparatus according to claim 1, whereinthe first detection unit and the second detection unit use an opticalsensor.
 7. The liquid ejection apparatus according to claim 6, whereinthe first detection unit and the second detection unit are configured toobtain the detection results based on a pattern included in the conveyedobject.
 8. The liquid ejection apparatus according to claim 7, whereinthe pattern is generated by interference of light irradiated on aroughness formed on the conveyed object; and the first detection unitand the second detection unit are configured to obtain the detectionresults based on an image capturing the pattern of the conveyed object.9. The liquid ejection apparatus according to claim 1, furthercomprising: a measuring unit configured to measure an amount of movementin the conveying direction of the conveyed object; wherein the liquid isejected based on the amount of movement measured by the measuring unitand the at least two detection results.
 10. The liquid ejectionapparatus according to claim 1, wherein the conveyed object is a longcontinuous sheet extending in the conveying direction.
 11. The liquidejection apparatus according to claim 1, further comprising: acalculating unit that is provided with respect to the each liquidejection head unit of the plurality of liquid ejection head units and isconfigured to calculate an amount of positional variation of theconveyed object by comparing the at least two detection resultsincluding a first detection result and a second detection result;wherein the movement control unit moves a liquid ejection head unit ofthe plurality of liquid ejection head units based on the amount ofpositional variation calculated with respect to the liquid ejection headunit; wherein the first detection result is detected by the firstdetection unit or the second detection unit that is installed upstreamof the liquid ejection head unit to be moved by the movement controlunit; and wherein the second detection result is detected by the firstdetection unit that is installed closest to the liquid ejection headunit to be moved by the movement control unit.
 12. The liquid ejectionapparatus according to claim 11, wherein the first detection result isdetected by the first detection unit or the second detection unit thatis installed immediately upstream of the liquid ejection head unit to bemoved by the movement control unit.
 13. The liquid ejection apparatusaccording to claim 1, wherein the first detection unit and the seconddetection are installed at positions that are equidistant from eachother.
 14. A liquid ejection system including at least one liquidejection apparatus, the liquid ejection system comprising: a pluralityof liquid ejection head units that are configured to eject liquid onto aconveyed object at different positions along a conveying path forconveying the conveyed object; a first support member that supports theconveyed object and is provided upstream of a landing position of theliquid ejected onto the conveyed object by a corresponding liquidejection head unit of the plurality of liquid ejection head units; asecond support member that supports the conveyed object and is provideddownstream of the landing position of the corresponding liquid ejectionhead unit; at least one first detection unit that is installed betweenthe first support member and the second support member and is configuredto detect a position of the conveyed object with respect to anorthogonal direction that is orthogonal to a conveying direction of theconveyed object; at least one second detection unit that is installedupstream of the first detection unit and is configured to detect theposition of the conveyed object with respect to the orthogonaldirection; and a movement control unit that is configured to move eachliquid ejection head unit of the plurality of liquid ejection head unitsbased on at least two detection results selected from a plurality ofdetection results output by the first detection unit and the seconddetection unit.
 15. A liquid ejection method that is implemented by aliquid ejection apparatus including a plurality of liquid ejection headunits that are configured to eject liquid onto a conveyed object atdifferent positions along a conveying path for conveying the conveyedobject; a first support member that supports the conveyed object and isprovided upstream of a landing position of the liquid ejected onto theconveyed object by a corresponding liquid ejection head unit of theplurality of liquid ejection head units; a second support member thatsupports the conveyed object and is provided downstream of the landingposition of the corresponding liquid ejection head unit; at least onefirst detection unit that is installed between the first support memberand the second support member and is configured to detect a position ofthe conveyed object with respect to an orthogonal direction that isorthogonal to a conveying direction of the conveyed object; and at leastone second detection unit that is installed upstream of the firstdetection unit and is configured to detect the position of the conveyedobject with respect to the orthogonal direction; the liquid ejectionmethod comprising: moving each liquid ejection head unit of theplurality of liquid ejection head units based on at least two detectionresults selected from a plurality of detection results output by thefirst detection unit and the second detection unit.